Studies in this laboratory are designed to elucidate the role of DNA repair processes in carcinogenesis and in neurodegeneration. Most studies have been conducted with cells from patients with xeroderma pigmentosum (XP), who have defective DNA repair plus multiple cutaneous malignancies and premature aging of sun-exposed skin and of the nervous system. Cells from patients with other primary degenerations are also being studied. These diseases include Alzheimer disease, Down syndrome, Cockayne syndrome, ataxia telangiectasia, Parkinson disease, Huntington disease, and retinitis pigmentosa. These studies are designed to elucidate the pathogenesis of these disorders and to develop diagnostic tests. We assess the biological effectiveness of DNA repair by: 1) analysis of chromosomal and chromatid aberrations in cells treated with DNA-damaging agents; and 2) determining the repair in transfected normal and patient cells of plasmids exposed to DNA-damaging agents.